1. Technical Field
This invention relates to an electron beam system and an electron beam measuring method capable of performing three-dimensional measurement of a sample with high precision, using a photographed sample image, and in particular to improvement in adjusting corrections made to an electron optical system of a scanning charged-particle beam device so as to be suitable for image measurement.
This invention relates to an electron beam system and a reference sample for an electron beam system capable of performing three-dimensional measurement of a sample with high precision, using a photographed sample image, and in particular to an electron beam system and a reference sample for an electron beam system capable of adjusting, when the beam or sample of a scanning charged-particle beam device is tilted, corrections made to the angle and magnification and corrections made to an electron optical system, at the time of 3D measurement, so as to be suitable for image measurement.
2. Related Art
In conventional scanning charged-particle beam devices such as scanning electron microscopes (SEM), off-axis aberration of electron lenses is corrected to increase resolution of images from the scanning electron microscopes or the like. Off-axis aberration of the electron lenses is corrected by compensating for spherical aberration, coma, curvature of field aberration, astigmatism, and image surface distortion aberration. For spherical aberration, Scherzer's theorem is known. It is known that spherical aberration cannot be reduced to zero in axisymmetric electron lenses used in the electron microscopes or the like, whether they are an electrostatic type or a magnetic type. Therefore, in order to compensate for spherical aberration, an aspherical mesh or aspherical form is used as the shape of an electrostatic electrode or magnetic pole.
On the other hand, in cases of a transmission electron microscope (TEM), the sample is tilted to obtain transmission images at different tilt angles, and stereo observation is performed using the images as right and left images. In cases of a scanning electron microscope (SEM), the sample or the electron beam is tilted to obtain reflection images at different tilt angles, and stereo observation is performed using the images as right and left images. In the field of semiconductor manufacturing equipment, an electron beam device and a data processing device for an electron beam device are proposed which are capable of appropriately processing stereo detection data obtained from an electron microscope to permit accurate and precise three-dimensional observation of an image of a sample and performing three-dimensional shape measurement of the sample based on the observation.
However, in measuring a sample such as a semiconductor chip or a silicone wafer, in particular, electron beam distortion or magnification distortion dependent on the directions of the tilt and height of the sample may be present. When electron beam distortion or magnification distortion is present in the measuring direction of the sample image, the precision in performing image measurement of the sample varies. In fine processing of semiconductor in recent years, the width of the patterns formed on a chip, for example, is as small as in the order of submicrons, and the margin of dimensional error acceptable in three-dimensional shape measurement has been increasingly small as compared with the past. Therefore, conventional methods for compensating for off-axis aberration of electron lenses such as spherical aberration cannot achieve the precision necessary for stereo image measurement.
In the 3D measurement of a sample such as a semiconductor chip or a silicone wafer, in particular, it is necessary to accurately find the tilt angle of the beam or sample and the magnification at the time of measurement and photographing. Also, there may be electron beam distortion or magnification distortion dependent on the directions of the tilt and height of the sample. When the tilt angle or magnification is not accurate or when electron beam distortion or magnification distortion is present in the measuring direction of the sample image, the values used in the image measurement of the sample are not correctly found and the precision further varies. In fine processing of semiconductor in recent years, the width of the patterns formed on a chip, for example, is as small as in the order of submicrons, and the margin of dimensional error acceptable in three-dimensional shape measurement has been increasingly limited as compared with the past. Therefore, conventional methods for the approximate tilt angle value or magnification and for compensating off-axis aberration of electron lenses such as spherical aberration cannot achieve the precision necessary for stereo image measurement.
This invention has been made to solve the foregoing problems, and it is therefore an object of this invention to provide an electron beam device and a reference sample for an electron beam device capable of performing image measurement of a sample with high precision, irrespective of the tilt angle and height of the sample.